The present invention relates to an operator distributing a granular material, in particular sand, from a fixed workstation. In particular, it relates to filling the bunkers, commonly known as xe2x80x9csand boxesxe2x80x9d that are provided on trains and trams. More precisely, the invention relates to apparatus for filling said sand boxes from a fixed workstation referred to as a xe2x80x9csand pointxe2x80x9d, while the boxes lie within a determined area surrounding said workstation.
Apparatus of the sand point type for distributing granular material is known, in particular from document EP 0 561 679, said apparatus having a transfer vessel for containing the material and a portable distribution head which is connected via a flexible hose to the transfer vessel, which vessel is fed with compressed air under pressure.
Such apparatus is generally part of a distribution installation having a plurality of fixed workstations, said installation also including a storage silo which is connected to and fills a plurality of storage vessels, each storage vessel being itself connected to and feeding a plurality of sand point type apparatuses as described above. The storage vessels and the sand point apparatuses can be placed on the ground, can possibly be buried, or they can be situated on raised gangways or supports.
When one or more trains are situated in the area situated close to a sand point, an operator fills the various sand boxes that are to be found in said zone by moving the distribution head of the sand point from one sand box to another. Nevertheless, this operation is restricted by the capacity of the transfer vessel of the sand point. When the level of sand in the vessel reaches a determined low threshold, sand can no longer be distributed properly to the distribution head so it becomes essential to interrupt the operation for the time required to fill the transfer vessel with sand coming from a storage vessel. This difficulty is of little importance when filing sand boxes of small capacity. However, it becomes unacceptable in countries where sand boxes are of larger capacity or where the number of sand boxes accessible from a given sand point is also large.
Naturally, to mitigate such a difficulty, it would suffice to increase the capacity of the sand point transfer vessel. Nevertheless, such an increase gives rise to other difficulties, in particular it is difficult to obtain continuous transfer without the sand jolting in the transfer hose connecting the transfer vessel to the portable distribution head. The greater the sand capacity of the transfer vessel, the greater the difficulty in controlling the compressed air pressure and flow rate conditions so as to obtain transfer under acceptable conditions of safety for the operator. In addition, in the event of an accident, e.g. the vessel being empty of sand and under air pressure because the low level was not detected, the discharge of air under pressure from the vessel presents risks of injuring the operator by a phenomenon identical to that of compressed air expanding in a hose that is not properly maintained. The greater the volume of the vessel, the higher the risk.
The object the Applicant seeks to achieve is to mitigate those drawbacks.
This object is fully achieved by the apparatus of the invention. The invention provides apparatus for distributing granular material, in particular sand, and comprising in a manner known from document EP 0 561 679:
a) a portable distribution head;
b) a flexible hose for transferring the material to the portable head;
c) a main feed duct for feeding material from a storage vessel; and
d) a main suction duct associated with the flexible hose for sucking dust from the portable head.
In a manner characteristic of the invention, the apparatus also comprises:
e) a plurality n of transfer vessels, each vessel:
being fed with material via a secondary feed duct fitted with a valve;
receiving, filtering, and exhausting suction air coming from the portable head via a secondary suction duct fitted with a valve;
delivering the material via a secondary delivery duct fitted with a valve; and
also being fitted with two sensors for sensing the level of the material, a high sensor and a low sensor;
f) three sets of multiple connections, the first set connecting the n secondary feed ducts to the main feed duct, the second set connecting the n secondary suction ducts to the main suction duct, and the third set connecting the n secondary delivery ducts to the transfer hose; and
g) control means connected to 3n valves and to the 2n level sensors, said means being programmed to make it possible to obtain substantially continuous operation of the distribution head based on alternating operation of the n transfer vessels by a changeover effect whereby one vessel is emptying while at least one other vessel is filling.
The number n of transfer vessels is generally two, or possibly three.
With two transfer vessels, operation takes place completely continuously with filling of a transfer vessel being transparent to the operator, providing, in operation, the rate material is fed to the vessel being filled is not less than the rate at which material is being removed via the distribution head. Nevertheless, even if this condition is not complied with in full, a combination of two transfer vessels of smaller volume operating in alternation makes it possible to work with a volume of material which is always greater than twice the capacity of two of said vessels.
In practices when the material drops below the threshold corresponding to said level, it is the low level sensor of the vessel that is being emptied which serves to trigger changeover of the control means causing firstly the distribution head to be fed from the other vessel and secondly the emptied vessel to be refilled. The high level sensor causes the valve in the secondary feed pipe-of the corresponding vessel to be closed once the material has reached the determined high level. An apparatus with two transfer vessels each having a volume of about 200 liters has been found to be sufficient for filling the sand boxes of locomotives of the type developed in North America which have a capacity of more than 700 liters, with two sand boxes at the front and one sand box at the rear of the locomotive, each sand box generally needing to be filled with half its capacity on each operation.
To minimize the amount of space occupied on the platform, the n secondary feed ducts, the n secondary suction ducts, the n secondary delivery ducts, the three multiple connection assemblies, the 3n valves, and the control means are preferably placed in a housing structure extending between the n transfer vessels, said vessels preferably being in the form of vertical axis cylinders.
Advantageously, the housing structure comprises a central post terminated by a substantially horizontal arm which supports the hose, which is pivotally mounted, and which has its free end situated perceptibly beyond the transfer vessels.
Another difficulty lies in the length of certain locomotives which can be as much as 25 meters (m) long, thus making it necessary to increase the length of the hose connecting the transfer vessel to the distribution head.
Another difficulty lies in the fact that in certain locomotives, particularly in North America, the inlet orifice to the sand box is not disposed on the side adjacent to the platform at man height, but is high up, requiring filling to be performed vertically.
Another object the Applicant seeks to achieve is to mitigate the above-mentioned difficulties. This object is fully achieved by a variant embodiment of the invention in which the secondary delivery duct is connected to the corresponding transfer vessel at the top thereof, via a delivery tube which penetrates obliquely into the inside of the vessel and whose open end is situated near the bottom thereof.
The transfer vessel is optionally fitted with additional air feed means close to said end of the tube. Thus, the additional air which is fed towards the end of the delivery tube fluidizes to some extent the material in the vicinity of the orifice of the tube corresponding to said end, thereby decompacting said material and facilitating transfer thereof into the tube even though the tube extends towards the top of the vessel. This additional air feed makes it possible to restrict the pressure of compressed air inside the transfer vessel to a maximum of 2 bars. Furthermore, when the connection between the hose and the transfer vessel takes place high up, via the second end of the tube that extends out from the vessel, then the length required for said hose is reduced when it comes to filling sand boxes having their filling orifices likewise situated high up.
For example, the delivery tube can be double-walled and the additional air feed can take place via the annular space between the two walls.
The suction air coming from the portable head is delivered into one of the transfer vessels via a secondary suction duct, and it is filtered and then exhausted in that vessel. In a particular disposition of the invention, the particles contained in the suction air coming from the portable head are recycled inside the transfer vessel into the granular material that is to be distributed. To obtain this result, the transfer vessel has a top filter compartment within which a filter is placed; the bottom of said filter compartment has a conical collector with a central outlet orifice that is fitted with a valve. In addition, the secondary suction duct opens out into the top filter compartment in the zone outside the filter while an air removal duct opens out into the zone inside the filter. When the transfer vessel is in operation, the valve closes the central orifice of the conical collector. The pressure that exists inside the transfer vessel is high enough to cause the granular material to be transferred via the secondary delivery duct. The air which is sucked in from the portable head passes through the filter before being removed to the outside of the transfer vessel. Dust contained in said sucked-in air is retained by the filter. When delivery of material from the transfer vessel is halted, particularly under the action of the low sensor, the valve fitted to the orifice of the conical collector opens, putting the top filter compartment of the transfer vessel into communication with the bottom compartment containing the granular material. During filling, following delivery, it is possible to proceed with unclogging sequences, each sequence consisting in rapidly opening a valve putting the inner zone of the filter into communication with a small supply of compressed air raised to a pressure of about 5 bars to 7 bars. This brief injection of compressed air serves to detach the particles held on the outer surface of the filter. Said particles then fall into the conical collector, pass through the open central orifice of said collector, and drop into the bottom compartment containing the granular material.
It is essential to avoid sudden decompression inside the transfer vessel since such decompression would run the risk of bursting the filter. For this purpose, it is preferable to use a solenoid valve which opens progressively, or indeed a decompression bypass or a calibrated orifice.